The invention relates to an engine in which instead of effecting the direct combustion of fuel in air in one stage of combustion, the fuel is reacted in a plurality of successive stages of which a first stage is an endothermic chemical reaction and a subsequent stage is an exothermic chemical reaction. Examples of gas turbine plant providing successive endothermic and exothermic chemical reactions are disclosed in British Pat. Specifications Nos. 1194586 of Motoren und Turbinen Union Munchen GMBH, 1138165 of M.A.N. Turbo GMBH and 923316 Maschinenfabrick Augsburg-Nurnberg A. G.